The objective of this work is to study proteases which are involved in the insertion of proteins into or through the E. coli cell envelope as well as those involved with turnover of these proteins. The following approaches are proposed: The study of turnover rates and degradation patterns of nitrate reductase in several classes of mutants lacking enzyme activity, as well as those grown under conditions which cause the production of defective enzyme. The purification and characterization of proteases isolated from the cytoplasmic membrane. The study of the insertion of the cytochrome-containing subunit of nitrate reductase into the cytoplasmic membrane using antibody to this protein to follow its biosynthesis during pulse-chase experiments.